In a typical electrostatographic printing apparatus, a light image of an original to be copied is recorded in the fonts of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles, which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which may be a photosensitive member itself or other support sheet such as plain paper, transparency, specialty coated paper, or the like.
The use of thermal energy for fixing toner images onto a support member is well known. In order to fuse electroscopic toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Typically, thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 90° C. to about 160° C. or higher, depending upon the softening range of the particular resin used in the toner. It is not desirable, however, to raise the temperature of the substrate substantially higher than about 200° C. because of the tendency of the substrate to discolor at such elevated temperatures particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means, including a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles generally takes place when the proper combination of heat, pressure and contact time are provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and they can be adjusted to suit particular machines, process conditions, and printing substrates.
Generally, fuser and fixing rolls are prepared by applying one or more layers to a suitable substrate. For example, cylindrical fuser and fixer rolls are typically prepared by applying an elastomer or a fluoroelastomer layer, with or without additional layers, to an aluminum core. The coated roll is then heated in a convection oven to cure the elastomer or fluoroelastomer material. Such processing is disclosed in, for example, U.S. Pat. Nos. 5,501,881, 5,512,409 and 5,729,813, the entire disclosures of which are incorporated herein by reference.
In use, important properties of the fuser or fixing members include thermal conductivity and mechanical properties such as hardness. Thermal conductivity is important because the fuser or fixer member must adequately conduct heat to provide the heat to the toner particles for fusing. Mechanical properties of the fuser or fixer member are important because the member must retain its desired rigidity and elasticity, without being degraded in a short period of time. However, increasing the loading of the filler tends to adversely affect mechanical properties of the coating layer, making the member harder and more prone to wear. For example, conventional metal oxides such as aluminum, iron, copper, tin, and zinc oxides may be used as fillers and are disclosed in U.S. Pat. Nos. 6,395,444, 6,159,588, 6,114,041, 6,090,491, 6,007,657, 5,998,033, 5,935,712, 5,679,463, and 5,729,813. These metal oxide filler materials, at loadings up to about 60 wt %, provide thermal conductivities of from about 0.2 to about 1.0 Wm−1K−1. However, as mentioned above, the loading amount of the filler must be limited due to the increased hardness provided by high loading levels.
Although excellent toner images may be obtained with fuser and fixing roils and members, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators, and printers are developed, there is a greater demand on print quality. Improved fixing member designs must target higher sensitivity, faster discharge, mechanical robustness, and ease of fabrication. The delicate balance in charging image and bias potentials, and characteristics of the toner and/or developer must also be maintained. This places additional constraints on the quality of fixing and fuser member manufacturing, and thus on the manufacturing yield. Fusing and fixing members are generally exposed to repetitive electrophotographic cycling, which subjects the exposed layer to mechanical abrasion, chemical attack and heat. This repetitive cycling leads to gradual deterioration in the mechanical and electrical characteristics of the affected layer(s), and often results in the formation of microcracks. In particular, structural polymers are susceptible to the formation of such cracks and/or microcracks, which often form at a depth within the structure such that detection and repair are impossible. Once such cracks have developed, they may significantly and permanently compromise the functionality of the fusing or fixing member.
Permanent damage to the fuser roll by contact with paper edges remains a major concern that leads to premature failure of the fuser roll. The replacement costs associated with failed fuser rolls is extremely high, and thus improving fuser roll lifespan will result in significant cost-savings.
Accordingly, there is a need in the art for improved fixing members that will respond to and correct material breakdown as it occurs. Thus, in an effort to extend the life of fixing member components to the lifetime of the machine, devices having the ability to respond to their environment and that are self-healing when damage occurs are desired. Such devices would eliminate the need to maintain the machine by either the customer or a technician. There is also a need for improved materials that will not hinder thermal conductivity, but of a type or at loading levels that provide lower hardness to the member and that improve other desirable mechanical properties of the member, such as extended performance. This disclosure is thus directed to a fuser roll that is capable of self-healing. One such method of achieving self-healing, for example, involves the incorporation of healing material in a layer of the fuser roll. Such healing materials may, for example, be encapsulated in microcapsules such that, in the event of wear or scratching of the fuser roll, the capsules rupture, thereby releasing the healing material, which then may react with an embedded catalyst, causing polymerization and damage repair or damage control.
Despite the various approaches that have been taken for forming fusing and fixing members there remains a need for improved fusing and fixing member design, to provide improved imaging performance and longer lifetime, reduce the need for maintenance, and the like.